1. Field of the Invention
The present invention relates to a method for the manufacture of a semiconductor device through the use of a semi-amorphous semiconductor.
The semi-amorphous semiconductor herein mentioned is defined as a semiconductor which is formed of a mixture of a microcrystalline semiconductor and a non-crystalline semiconductor and in which the mixture doped with a dangling bond neutralizer and the microcrystalline semiconductor has a lattice strain.
2. Description of the Prior Art
In a semiconductor device using the semi-amorphous semiconductor, the semi-amorphous semiconductor formed in the shape of a layer provides a large optical absorption coefficient as compared with a single crystal semiconductor. Accordingly, with a semi-amorphous semiconductor layer of sufficiently smaller thickness than the layer-shaped single crystal semiconductor of the semiconductor device using the single crystal semiconductor, it is possible to achieve a higher photoelectric conversion efficiency than that obtainable with the single crystal semiconductor device.
Further, in the semi-amorphous semiconductor device, the semi-amorphous semiconductor provides a high degree of photoconductivity, a high degree of dark-conductivity, a high impurity ionization rate and a large diffusion length of minority carriers as compared with an amorphous or polycrystalline semiconductor. This means that the semi-amorphous semiconductor device achieves a higher degree of photoelectric conversion efficiency than an amorphous or polycrystalline semiconductor device.
Accordingly, the semi-amorphous semiconductor device is preferable as a semiconductor photoelectric conversion device.
For the manufacture of the semi-amorphous semiconductor device, there has heretofore been proposed a method including a step of forming the semi-amorphous semiconductor in the shape of a layer or a substrate by the glow discharge method or plasma CVD method employing a gas of hydride of a semiconductor material, such as silane (SiH.sub.4) gas, a gas of halide of a semiconductor material, such as silicon tetrafluoride (SiF.sub.4) gas, and a gas of hydride and halide of a semiconductor material, such as dichlorosilane (SiH.sub.2 Cl.sub.2).
With such a conventional method, the semi-amorphous semiconductor forming the semi-amorphous semiconductor device can be formed containing hydrogen and/or halogen as a dangling bond neutralizer. Accordingly, as compared with the case of containing no hydrogen and/or halogen, the semi-amorphous semiconductor can be obtained containing an extremely small number of dangling bonds which serve as minority carrier recombination centers; namely, the semi-amorphous semiconductor can be obtained containing a markedly small number of recombination centers.
With the abovesaid prior art manufacturing method, however, the number of recombination centers contained in the semi-amorphous semiconductor is as large as about 10.sup.17 to 10.sup.19 /cm.sup.3.
Further, in a semiconductor photoelectric conversion device, it is desirable, in general, that the diffusion length of the minority carriers of the semiconductor be approximately 1 to 50 .mu.m which is intermediate between 300 A which is the diffusion length of the minority carriers of an amorphous semiconductor and 10.sup.3 .mu.m which is the diffusion length of the minority carriers of a single crystal semiconductor.
With the abovesaid conventional manufacturing method, however, since the semi-amorphous semiconductor is formed containing as large a number of recombination centers as about 10.sup.17 to 10.sup.19 /cm.sup.3, the diffusion length of the minority carriers of the semi-amorphous semiconductor cannot be set to the abovementioned desirable value of about 1 to 50 .mu.m.
Therefore, according to the prior art manufacturing method, the semi-amorphous semiconductor can be obtained to have a photoelectric conversion efficiency as low as only about 2 to 4%.